HIB fractures increase exponentially with advancing age. Major risk factors include 1) increased frequency of falls and 2) decreased bone mineral density (BMD). Decline in lean muscle mass is associated with both decreased activity and increased age. BMD also declines with lack of physical stress on the bone. An aerobic/resistance exercise program which includes stair-climbing and level walking is designed to increase BMD of the femur, muscular strength of the quadriceps and cardiovascular fitness in elderly women. Mechanical stress can be exerted on the femur through increased weight and muscular pull. The purpose of this study is to evaluate the ability of elderly women to reduce or eliminate the decline in BMD through increased muscular strength and weight-bearing exercise. The study will include 20 exercising and 10 nonexercising women over 65 years of age. The exercise program will include 15-20 min of warm-up, 20-30 min of aerobic/resistance work, and a 10 min cool-down. The aerobic/resistance segment will consist of two tasks, level walking and stairclimbing in a ratio of 2:1 (e.g. 6 min. level walking: 3 min. stair climbing). Progressive resistance will be achieved through weighted (back-pack) stair-climbing. The cardiovascular intensity will begin at 40% of the pre-training maximal heart rate, gradually increasing to 70% by the fifth month of training. The subjects will volunteer to meet 3/x per week for 10 months. Pre- and post-training measurements will include maximal oxygen consumption using an incremental treadmill test: Vastus lateralis muscle fiber typing and area measures: quadriceps isometric and isokinetic strength measures: and BMD (dual photon absorptiometry) of the proximal femur, proximal tibia and lumbar spine (L2-L4). Mid-training (5-months) testing will include strength and BMD measures. Pre- to post-training differences will be analyzed for statistical differences by analysis of covariance.